The present invention relates to alloys having a metallic iron content for use in the manufacture of iron and steel as well as the method of making such alloys.
In the manufacture of iron and steel, it is customary to make certain additions to the melting furnace such as various metalliferous products in the form of alloys such as ferrosilicon, ferronickel, ferrochrome, ferromanganese, and the like. Such ferroalloys normally contain a substantial amount of carbon. In the present invention, metallized iron, the alloy element in oxide form, and carbon are formed into a compact, or briquet, then charged into a shaft furnace along with additional carbonaceous material such as coke, if necessary, and reduced to form a molten ferroalloy product of high value for foundry practice and other iron and steelmaking uses.
"Metallized iron", as used throughout this specification does not mean coated with iron metal, but means substantially completely reduced to the metallic iron state, i.e., always in excess of 60% of the total iron is present in metallic form, with the remainder of the iron being present in the oxide form, but usually in excess of 80% of the total iron in the material is present as metal. Such metallized iron in many forms, including pellets, is well suited as feed material to steelmaking furnaces such as an electric arc furnace.
The briquet to be charged to the shaft furnace preferably employs metallized iron fines as the basic ingredient in its composition. Previously known briquets employ iron oxide fines. The presence of metallized fines reduces the energy requirement for the invented process. Since the iron fines are in the metallized condition, the energy normally required for reducing iron oxide to iron is not a requirement in this process. Since the iron in the briquet need not be reduced before melting, the energy requirement is reduced.
The closest known prior art patents include Rehder U.S. Pat. No. 4,179,283, Merkert U.S. Pat. No. 4,395,284, Strange U.S. Pat. No. 4,369,062, Gustaffson U.S. Pat. No. 2,010,230, and Querengasser, et al. U.S. Pat. No. 3,431,103.
Rehder teaches the briquetting of metal oxides only and has no direct reduced iron in his briquet charge. He utilizes two sources of carbon, a high reactivity and a low reactivity carbon.
Merkert teaches that iron and a binder are optional and are not essential ingredients. He prepares porous compacts for use as a feed material to an electric furnace, the material having an apparent low density and high internal porosity. Merkert states that up to about 15% of the silica weight can be iron particles, however, this is identified as mill scale, which is generally in oxide form.
Strange teaches production of a briquet from reclaimed materials, such as iron fines and mill scale up to 41%. A study has shown that he has insufficient carbon in his briquet to reduce the mill scale. He also requires an additional source of energy to provide heat during the melt.
Gustafsson teaches use of a thermit reducing agent, which provides both reduction and heat, and increases cost of operation of the process, and further uses insufficient carbon to effect complete reduction of iron oxide, whereas the present invention utilizes carbon as a reducing agent, and provides heat in a more economical manner.
Querengasser requires a critical combination of coal with a caking capacity of 4 to 10, and non-caking coal or coke. In addition, Querengasser states that ferrosilicon is made from iron turnings or chips, quartz, and carbon. He states also that iron oxide is less suitable than iron turnings or chips for making high grade ferrosilicon.
The present invention differs from each of these prior art teachings in that the charged briquets contain the desired alloy metal in oxide form, carbon, and iron which is from 60% to 97% metallized.